Cerebral palsy (CP) is a neurological disorder of development affecting more than 750,000 people in the US (1). A common source of morbidity in this condition is gait disorders, with crouch gait being one of the most common forms (3). Crouch is a fatiguing gait (4-5), characterized by excessive knee flexion during stance (6-7), that often requires surgical correction to allow patients to continue to ambulate as they mature (8). Distal femoral extension osteotomy coupled with patellar tendon advancement (DFEO + PTA) is a promising surgical approach for reducing crouch and restoring quadriceps strength in these children (2, 9). While short term outcomes are generally good, little is known about the why the coupled procedures are better than either procedure alone, and which surgical parameters are most efficacious. Perhaps more importantly, the long term implications of the procedures on skeletal growth and cartilage health are unclear (10). This project aims to use musculoskeletal modeling, dynamic magnetic resonance imaging (MRI), and gait analysis techniques to investigate the influence of DFEO + PTA on knee extensor mechanics. Surgical simulations will be performed on computer models of the musculoskeletal system to gain insights into how the degree of osteotomy and patellar advancement affects muscle moment arms, muscle operating lengths, and knee extensor strength post-surgery. A novel dynamic MRI technique (11) will then be used to discover changes in kinematics and cartilage contact that can result from the substantial surgical corrections. Finally, gait analysis will be coupled with computational models to relate surgically induced changes in joint mechanics to functional gait performance. The anticipated outcome is a scientific understanding of the surgical effects on the musculoskeletal system, which can be used to mitigate the potential for adverse outcomes in both the short- and long-term. Through the completion of this project as part of this fellowship, Rachel Lenhart will be exposed to many areas of experimental and computational biomechanics research. Her training plan also includes coursework in mechanical and biomedical engineering to develop her technical skills to compliment her formal medical training. Given that her end goal is to be a successful physician scientist, development of clinical and communication skills will also be a focus. Through consistent participation in the clinic, continual practice and feedback on writing and presentation abilities, and regular meetings with her sponsors and advisory team, Rachel will be poised for success both as a pediatric orthopedic surgeon and as an independent biomechanics researcher.